1. Field of the Invention
The present invention relates to an apparatus for determining emergency conditions of a vehicle, and particularly to an apparatus for determining emergency conditions of a vehicle, which detects a sudden impact of a vehicle and actuates a passenger safety device.
2. Description of the Related Art
Conventionally, an apparatus for determining emergency conditions of a vehicle has been employed in which, when it is determined that there is a need to protect a passenger by detecting a sudden impact on a vehicle, a signal is outputted which actuates a passenger safety device, such as the expansion of an air bag, for protecting a passenger.
As a method for detecting a sudden impact on a vehicle, one is known in which determination as to whether it is necessary to protect a passenger is done by detecting vehicle acceleration. In an apparatus for determining emergency conditions of a vehicle using this method, a signal is obtained by making it such that when a time integral of an output signal from an acceleration sensor located in a vehicle exceeds a predetermined value at the time of a vehicle collision, an expansion signal for expanding an air bag is outputted. The air bag is thereby expanded, so that a passenger can be protected at the time of a vehicle collision.
Thus, a time standard from the time of collision which is most suitable for expanding an air bag (hereinafter referred to as an air bag expansion time standard) is previously determined. The above-described predetermined value is set so that the expansion signal for expanding an air bag is outputted between an upper limit time and a lower limit time of the air bag expansion time standard.
However, an acceleration sensor provides output signals of different wave forms depending upon conditions of the vehicle collision. For example, when a vehicle collides head-on with another(hereinafter referred to as "time of a vehicle head-on collision"), an output signal of a short-time, high-G wave form (i.e., a high-frequency and high-amplitude wave form in which a large acceleration is applied in a short time) is provided. On the other hand, when one of the side surfaces of a vehicle has been hit by another vehicle (hereinafter referred to as "time of an off-set collision"), an output signal of a long-time, low-G wave form (i.e., a low-frequency and low-amplitude wave form in which a small acceleration is applied for a long time) is provided. Only by making an integration of this output signal from the acceleration sensor in a conventional manner to make a determination may cause the degree of freedom of determination to be decreased. As a result, it was not possible to make a determination, at the same time, of whether the air bag expansion time standard corresponding to the short-time, high-G wave form at the time of a vehicle head-on collision had been satisfied nor whether the air bag expansion time standard corresponding to the long-time, low-G wave form at the time of an off-set collision had been satisfied. Thus, a conventional apparatus for determining emergency conditions of a vehicle has not been able to correspond to inconsistent time standards, because the characteristics of the wave forms are different from each other.
On the other hand, since the acceleration sensor detects all areas of vehicle acceleration, such conventional apparatus for determining emergency conditions of a vehicle may erroneously judge that vehicle acceleration generated in a short time during running on a rough road is a vehicle collision. In order to solve this problem, an air bag is required which expands only at the time of a vehicle collision and not when running on a rough road or the like.
With the above-described facts in view, it is an object of the present invention to provide an apparatus for determining emergency conditions of a vehicle, which is capable of making a proper determination to actuate a passenger safety device at the most suitable time in a condition requiring the passenger safety device irrespective of the vehicle conditions or the conditions of a vehicle collision.